Displaying Error Messages with the message and messages Tags

The message and messages tags are used to display error
messages when conversion or validation fails. The message tag
displays error messages related to a specific input component, whereas the messages tag displays the error messages for the entire page.

The for attribute
refers to the ID of the component that generated the error message. The error
message is displayed at the same location that the message tag
appears in the page. In this case, the error message will appear after the
Submit button.

The style attribute
allows you to specify the style of the text of the message. In the example
in this section, the text will be red, New Century Schoolbook, serif font
family, and oblique style, and a line will appear over the text. The message
and messages tags support many other attributes for defining styles. Please
refer to the TLD documentation for more information on these attributes.

Another attribute the messages tag supports is the layout attribute. Its default value is list,
which indicates that the messages are displayed in a bulleted list using the
HTML ul and li elements. If you set
the attribute to table, the messages will be rendered in
a table using the HTML table element.

The preceding example shows a standard validator is registered on input
component. The message tag displays the error message associated with this
validator when the validator cannot validate the input component’s value.
In general, when you register a converter or validator on a component, you
are queueing the error messages associated with the converter or validator
on the component. The message and messages tags
display the appropriate error messages that are queued on the component when
the validators or converters registered on that component fail to convert
or validate the component’s value.

All the standard error messages that come with the standard converters
and validators are listed in section 2.5.4 of the JavaServer Faces specification.
An application architect can override these standard messages and supply error
messages for custom converters and validators by registering custom error
messages with the application by means of the message-bundle element
of the application configuration file. Referencing Error Messages explains more about error messages.